DE2601141C2 - Modified oil-based lubricant for internal combustion engines and method for improving the operation of an internal combustion engine - Google Patents

Description

The present invention relates to a modified oil-based lubricant for an internal combustion engine equipped with an oil filter, containing a major amount of a liquid lubricating oil mixed with a minor amount of an additive.

The main pollutants in the exhaust gases of internal combustion engines are nitrogen oxides, unburned hydrocarbons and carbon monoxide. The ecological problems caused by this are not only due to the pollution of the atmosphere by the exhaust gases, but also to the fact that the substances emitted cause chemical reactions in the atmosphere when exposed to the sun's radiant energy. The so-called photochemical smog that occurs in many large cities is the result of photochemical reactions involving hydrocarbons from exhaust gases, evaporation losses and nitrogen oxides.

Some of the factors that play a role in the emission of pollutants are discussed in more detail below.

Combustion chamber residues

The exhaust emission of new vehicles undergoes a significant change during the first 8,000 to 16,000 kilometers of operation. The reason for this change is the formation of deposits on the walls of the combustion chambers. These deposits act like sponges and absorb hydrocarbons during the compression movement of the cylinder, whereby the hydrocarbons are preserved within the pores of the deposits during the combustion process and are then emitted into the atmosphere as unburned hydrocarbons during the exhaust process. As these deposits build up as the mileage of the machine increases, the level of hydrocarbon emission also increases to a level that gives rise to complaints.

Mixture influence

The ratio of air to fuel in the fuel mixture has a significant effect on the emission of hydrocarbons in the exhaust gas. It has been found that the emission of unburned hydrocarbons and carbon monoxide can be significantly reduced by depositing the mixture, since the oxygen to fuel ratio is then high and complete combustion takes place. The reduction in hydrocarbon emissions brought about by operating the engine on lean mixtures is accompanied by better fuel economy. However, a lean mixture usually results in engine "knocking" which is a practical limitation on the reduction in hydrocarbon emissions that could otherwise be achieved.

idle

The speed at which an engine idles determines the emission output. While a reduced idle speed is highly desirable, it is not possible with current lubricants to reduce the idle speed sufficiently to achieve minimal emissions without causing the engine to sputter to an unacceptable level.

It must be taken into account that due to the constant starting and stopping of public and private transport in urban traffic, a lot of the operating time of the vehicles is spent idling, which contributes to a high level of pollutant emissions into the atmosphere. contributes.

The invention is based on the object of developing a lubricant that allows a high boundary layer lubrication and thus reduces friction and heating of the interfaces to a minimum.

• a) einer Dispersion von Polytetrafluoräthylenteilchen (PTFE) im Größenbereich unterhalb eines Mikrons sowie
• b) einem Stabilisierungsmittel für die Dispersion besteht, wobei das Stabilisierungsmittel in Form eines die Ladung neutralisierenden Mittels ein Agglomerieren und Koagulieren der Teilchen der Dispersion verhütet und somit ein Hindurchlaufen des Schmiermittels durch das Ölfilter ohne Abtrennung der Teilchen aus dem Öl bewirkt.

This object is achieved according to the invention by using an additive consisting of

• a) a dispersion of polytetrafluoroethylene (PTFE) particles in the sub-micron size range and
• b) a stabilising agent for the dispersion, the stabilising agent being in the form of a charge neutralising agent which prevents agglomeration and coagulation of the particles of the dispersion and thus enables the lubricant to pass through the oil filter without separating the particles from the oil.

Modified lubricants with a PTFE-based additive for internal combustion engines equipped with an oil filter were previously unknown:

According to GB-PS 10 39 295, polytetrafluoroethylene particles in a liquid medium that can be evaporated at atmospheric pressure are used to coat surfaces with PFTE.

US-PS 38 47 887 relates to a process for the preparation of hydroxy derivatives of fluorinated polymers and their use as antistatic fuel components.

US-PS 38 47 826 refers to a non-liquid antifriction composition consisting of PTFE and a copper sulfite, which additionally contains filler.

US-PS 38 06 455 discloses a process for preparing a lubricating oil composition consisting of a base lubricating oil, a dispersant, fluorinated polystyrene or polypropylene and a polyhalogenated methane or ethane.

It is essential that the polytetrafluoroethylene is evenly dispersed in the oil in the form of microfine particles without the particles agglomerating. The polytetrafluoroethylene particles must pass easily through an oil filter and between closely spaced machined metal surfaces such as those found in hydraulically operated valve tappets.

The following table shows various particle sizes of commercially available polytetrafluoroethylene: °=c:60&udf54;&udf53;vu10&udf54;&udf53;ta:6:13.6:18&udf54;&udf53;tz5.5&udf54;&udf53;tw.4&udf54;&udf53;sg8&udf54;\Manufacturer\Product\Particlesize&udf53;tz5.10&udf54;&udf53;tw.4&udf54;&udf53;sg9&udf54;\Whitcon\PTFE powder\under 1¤Óm&udf53;tz&udf54; \Liquid Nitrogen&udf50;Corp.\ PTFE powder\ 8^10¤Óm&udf53;tz&udf54; \Du Pont\ PTFE dispersions\ 0.05^0.5¤Óm&udf53;tz&udf54;&udf53;te&udf54;&udf53;vu10&udf54;

The unusually small particle size of Du Pont products makes this material best suited for boundary layer lubrication.

Polytetrafluoroethylene dispersions, such as those commercially available, are very unstable. According to Du Pont company literature, PTFE dispersions "settle on prolonged standing or heating above 65.5°C. The material may be redispersed by gentle agitation. Stocks stored for an indefinite period should be redispersed at least every two weeks by inverting or rolling the container. High speed or vigorous agitation should be avoided as this will cause irreversible coagulation. The dispersion should be protected from the atmosphere to prevent coagulation by drying. The dispersion should be protected from freezing at all times to prevent irreversible coagulation."

The above-mentioned PTFE dispersions and similar aqueous dispersions are hydrophobic colloids with negatively charged particles. A dispersion in which 60% is in the form of solids contains about 0.9 g of polytetrafluoroethylene per cc of solution.

It has been found that by adding a silane or silizane, such as an aminosilane or methyltrichlorosilane, the resulting dispersions are remarkably stable to freezing and thawing. Although the reason for this stability is not known, it is believed that a cloud of silane atoms attaches itself to each of the polytetrafluoroethylene particles and, by neutralizing the surface charge, prevents the particles from clumping together. Thus, the silane acts as a charge neutralizer.

If 300 cc of a dispersion of polytetrafluoroethylene were mixed with 30 cc of a functional aminosilane or hexamethyldisilizane, a strongly alkaline compound which releases ammonia when wet, the dispersion can be repeatedly frozen and thawed without any change in properties. The dispersion can be dispersed in water, oil, emulsion paints and varnishes as often as desired, since the silane prevents coagulation by contact of the particles with one another. The best results were obtained with a ratio of 300 cc of the above polytetrafluoroethylene dispersion to 15 cc of silane or silizane. A smaller ratio leads to a certain degree of irreversibility, while a ratio of 50:50 results in irreversible gelation, since the silane competes with the polytetrafluoroethylene particles for water.

When the stabilized dispersion of polytetrafluoroethylene is mixed with a lubricant, the oil acts as a hydrodynamic lubricant at moderate and high speeds of the lubricated vehicle. At low speeds with high loads, where the oil is usually not effective, the tetrafluoroethylene polymer particles coat the metal surfaces and form a solid boundary layer lubricant which reduces friction and keeps heat generation to a minimum.

Another useful stabilizing agent is very finely divided aluminum oxide. A commercial product consists of particles with dimensions of about 0.01 µm, which are clumped together to form aggregates of 0.1 µm in size. They are among the few particles that have a positive surface charge up to a pH value of 9.1, the isoelectric point. Suspensions that have a negative charge are obtained by adjusting the pH value above 10, so that when dispensing Ammonia from the silizanes in the mixtures causes the aluminum oxide particles of polytetrafluoroethylene to migrate and neutralize the charge and prevent or control clumping. This has been tested and found to be correct, although the same effect is not achieved in terms of freezing and thawing properties as is the case with the silizanes or silanes.

In the manufacture of lubricants from oil and polytetrafluoroethylene, the thixotropy of the mixture is promoted by the use of alumina. The discrete particle shape makes it easier to maintain the particle shape and there is less tendency for the lubricant to spread into films.

Process for the addition of fluorocarbon dispersions to crankcases of internal combustion engines

It is important that the total concentration of dispersed fluorocarbon added to an internal combustion engine is very small. If the particles are not far apart and are in the form of discrete particles, there is a tendency for plates and lumps to form which can cause difficulties in hydraulic valve lifters. In addition, the agglomerated particles are easily removed by the oil filter.

• A. Es werden 200 ccm einer Dispersion von Polytetrafluoräthylen genommen und 20 ccm Hexamethyl-disilizan zugegeben. Es wird ein sehr flüssiges Produkt erhalten, das sich leicht in Öl usw. dispergiert.
• B. Es werden 0,95 l Maschinenöl (beliebiger Art) mit 20 ccm eines funktionellen Aminosilans versetzt, z. B. mit γ-Aminopropylsilan.
• C. Die beiden Stoffe A und B werden vermischt, wobei eine feine milchige Dispersion erhalten wird. Das Dispersionswasser des das PTFE enthaltenden Gemisches hydrolysiert das Silan, wodurch ein feines Netzwerk von Molekülen gebildet wird, das die Teilchen aus Polytetrafluoräthylen schützt und voneinander trennt. Es besteht eine leichte Neigung zum Absetzen, jedoch wird schon beim sanftesten Rühren eine erneute Dispergierung erzielt.

The following procedure for adding dispersions has proven to be effective in practice:

• A. Take 200 cc of a dispersion of polytetrafluoroethylene and add 20 cc of hexamethyldisilizane. A very fluid product is obtained which disperses easily in oil, etc.
• B. 0.95 l of machine oil (any type) is mixed with 20 cc of a functional aminosilane, e.g. γ- aminopropylsilane.
• C. The two substances A and B are mixed to obtain a fine milky dispersion. The dispersion water of the mixture containing the PTFE hydrolyses the silane, forming a fine network of molecules that protects and separates the polytetrafluoroethylene particles. There is a slight tendency for settling, but even the gentlest stirring will cause re-dispersion.

The solution is still far too concentrated for engines, but is superior as a lubricant for differential gears and high shear systems where there are no small orifices. Use in engines: Add approximately 200 cc of the solution mentioned to a cold engine (4.75 litres of oil) and then run the engine to distribute and disperse the fluorocarbon particles through the system.

It is now found that the engine always runs more smoothly when the internal surfaces have acquired a coating of polytetrafluoroethylene. There is a tendency for the oil filter to remove the larger particles and any clumps that may have formed, but sufficient polytetrafluoroethylene remains in circulation to repair the damaged surfaces and to maintain very good internal lubrication.

The engine can now be allowed to idle at very low speeds, first adjusting the idle jet of the carburettor so that the running appears somewhat rough, then turning the jet back and adjusting the final idle using the throttle adjustment screw.

The water present in the mixture is evaporated after the engine has reached operating temperature, keeping the fluorocarbon particles and the hydrolyzed silane in circulation. The silanes are very surface active and undoubtedly increase the lubricity of the entire system. The technology for preventing settling using protective colloids is well known and does not need to be explained in more detail.

The importance of the pressurized lubricant for engines is that most of the pollutant emissions in urban areas are caused by engines in traffic idling. If the engines were idling at half the normal speed, less pollutant would be blown out of the exhaust pipes. In addition, considerable savings in fuel should be achieved.

If the idling speed of the engine is set at about 350 to 400 rpm, which is considerably lower than the usual value prescribed by the manufacturers as the idling speed, and if the leanness of the fuel-air mixture is set at the optimum value for smooth idling operation, the emission of pollutants is reduced to a markedly low level. However, if air is admitted into the engine which is excessively hot and expanded, the leanness of the mixture is adversely affected. It is therefore desirable to introduce air in a relatively cool condition. For this purpose, the engine may be provided with a thermostatically controlled device by which the air inlet is opened directly to the atmosphere when the temperature of the air being sucked in exceeds a predetermined value.

The viscosity of the oil used in conjunction with the additive should be such that the oil pressure in a warm and disengaged engine remains at about 1.4 to 2.1 bar when the engine is idling at low speed (350 rpm). Fortunately, available multigrade oils with multiple viscosities (10-30, -40, etc.) contain wound chain or spiral chain polymers which expand or open under the influence of heat to increase the viscosity of the oil. This provides a low viscosity when cold for easier starting and a high viscosity when hot to maintain oil pressure. An additive of this invention can be used in such oils together with suitable protective colloids and detergents to maintain good dispersion in the crankcase. In some cases, suitable thickeners such as a polybutane can be added to the oil.

Claims (7)

1. Modified oil-based lubricant for an internal combustion engine equipped with an oil filter, containing a larger amount of a liquid lubricating oil mixed with a smaller amount of an additive, characterized in that the additive consists of
a) a dispersion of polytetrafluoroethylene particles in the size range below 1 µm and b) a stabilising agent for the dispersion, the stabilising agent being in the form of a charge neutralising agent which prevents agglomeration and coagulation of the particles of the dispersion and thus enables the lubricant to pass through the oil filter without separating the particles from the oil.
2. Modified oil lubricant according to claim 1, characterized in that the particles of polytetrafluoroethylene are present in aqueous dispersion and have a size of 0.05 to 0.5 µm. 3. Modified oil lubricant according to claim 1 or 2, characterized in that silanes or silizanes are used as stabilizing agents. 4. Modified oil lubricant according to claim 3, characterized in that a combination of hexamethyldisilizane and a functional aminosilane is used as the stabilizing agent. 5. Modified oil lubricant according to one of the preceding claims, characterized in that very finely distributed aluminum oxide (Al₂O₃) is used as the stabilizing agent. 6. A method for improving the operation of an internal combustion engine, characterized in that first a small but effective amount of an aqueous dispersion of polytetrafluoroethylene particles in the size range below 1 µm and a stabilizer for the dispersion to prevent agglomeration and coagulation of the particles in the form of a charge neutralizing agent are added to the ordinary lubricating oil for the engine, thereby providing the oil with boundary layer lubricating properties, then the idling speed of the engine is throttled to below the prescribed range and the air/fuel mixture for the engine is leaned out and thereby considerably reduced the emission of pollutants from the engine. 7. A method according to claim 6, characterized in that relatively cool air is sucked into the engine and the air/fuel mixture is thereby produced.